media: i2c: mt9v111: fix incorrect type for ret

Change "ret" from unsigned int to int type in mt9v111_calc_frame_rate()
to store negative error codes or zero returned by __mt9v111_hw_reset()
and other functions.

Storing the negative error codes in unsigned type, doesn't cause an issue
at runtime but it's ugly as pants.

No effect on runtime.

Signed-off-by: Qianfeng Rong <rongqianfeng@vivo.com>
Fixes: aab7ed1c ("media: i2c: Add driver for Aptina MT9V111")
Cc: stable@vger.kernel.org
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>